Crystal structure of anhydrous tripotassium citrate from laboratory X-ray powder diffraction data and DFT comparison.

Alagappa Rammohan,James A Kaduk

doi:10.1107/s2056989016011506

Abstract

The crystal structure of anhydrous tripotassium citrate, [K3(C6H5O7)] n , has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques. The three unique potassium cations are 6-, 8-, and 6-coordinate (all irregular). The [KO n ] coordination polyhedra share edges and corners to form a three-dimensional framework, with channels running parallel to the c axis. The only hydrogen bond is an intra-molecular one involving the hy-droxy group and the central carboxyl-ate group, with graph-set motif S(5).

Highlights

The crystal structure of anhydrous tripotassium citrate, [K3(C6H5O7)]n, has been solved and refined using laboratory X-ray powder diffraction data, and optimized using density functional techniques
Atoms are represented by 50% probability spheroids
The [KOn] coordination polyhedra share edges and corners to form a three-dimensional framework (Fig. 3), with channels running down the c axis

Summary

Chemical context

In the course of a systematic study of the crystal structures of group 1 (alkali metal) citrate salts to understand the anion’s conformational flexibility, ionization, coordination tendencies, and hydrogen bonding, we have determined several new crystal structures. Most of the new structures were solved using powder X-ray diffraction data (laboratory and/or synchrotron), but single crystals were used where available. The general trends and conclusions about the 16 new compounds and 12 previously characterized structures are being reported separately (Rammohan & Kaduk, 2016a). Five of the new structures, viz. NaKHC6H5O7, NaK2C6H5O7, Na3C6H5O7, NaH2C6H5O7, and Na2HC6H5O7, have been published recently (Rammohan & Kaduk, 2016b,c,d,e; Rammohan et al, 2016), and two additional structures, viz. KH2C6H5O7 and KH2C6H5O7(H2O), have been communicated to the Cambridge Structural Database The asymmetric unit of the title compound, showing the atom numbering. Atoms are represented by 50% probability spheroids

Structural commentary

Supramolecular features

Database survey

Synthesis and crystallization

DFT calculations